Liquid crystals (LC) are the materials of choice in many electro-optic applications and their use in building electrically tunable LC lenses (TLCLs) has been studied for decades [see S. Sato, “Applications of Liquid Crystals to Variable-Focusing Lenses,” Optical Review, Vol.6, No.6 (1999) 471-485]. Since the fabrication of flat substrates (coated by flat conductive and LC-alignment layers) is the most cost-effective way to manufacture LC cells, the main effort of the research and engineering community has been devoted to different ways of obtaining TLCL operation by using flat elements. Non-uniform LC gap and hole patterned electrodes, embedded glass lens [B. Wang, M Ye, S. Sato, “Lens of electrically controllable focal length made by a glass lens and liquid-crystal layers,” Applied Optics, V.43, No. 17, pp. 3420-3425, 2004], modal control [A. F. Naumov, M. Yu. Loktev, I. R. Guralnik, G. Vdovin, “Liquid-crystal adaptive lenses with modal control,” Optics Letters, V23, No. 13, pp. 992-994, 1998], polymer stabilized [V. V. Presnyakov, K. E. Asatryan, and T Galstian, A. Tork, Tunable polymer-stabilized liquid crystal microlens, Optics Express, Vol. 10, No. 17, pp. 865-870, 2002] and dielectric hidden layer [T. Galstian, V. Presniakov, K. Asatryan, “Method and Apparatus for spatially modulated electric field generation and electro-optical tuning using liquid crystals,” USA Patent Application 20070229754, 3 Mar. 2006] are some of the approaches that have been studied and documented to date. Each of these approaches has its advantages and drawbacks; however, the industry is presently imposing severe criteria of choice which makes many of them useless for many consumer devices, such as cell phones. Among other key requirements, the speed of the device and its reliability must be emphasized.
Except for some specific cases, the influence of magnetic field on materials is usually smaller than the influence of electric field. Also, the well known methods of magnetic field generation are mainly based on the use of optically non transparent materials and/or electromagnetic coils. That is why many optical modulators are applying electric fields as the excitation means, rather than magnetic fields. This is also the case for standard LC cells and LCDs too.
It is however well known that the magnetic field may be a tool to control the orientation of the director (average orientation of long molecular axes) of LC materials, via the so called Fredericksz effect. Accordingly, there have been some attempts to use the magnetic field in LC modulators. One example of such use is for building a polarization rotator [R. L. McAdams, “Liquid crystal polarization reorientation cell having magnetic field-applying coils,” U.S. Pat. No. 4,768,862, Sep. 6, 1988] using a “free-space” magnetic source, which is not optically transparent (and thus is made in a way to be out of optical path). Another interesting example is disclosed in U.S. Pat. No. 4,214,819 [L. Pohl, R. Eidenschink, J. Krause, G. Weber, “Electro-optical modulator,”, Jul. 29, 1980], whereby the response time of liquid crystal displays (LCDs) is accelerated by using a combination of electric and magnetic fields. More specifically, optically transparent magnetic field sources are embedded in the LC cell to accelerate the response time of LCDs.